1. Field of the Invention
The present invention relates to a spherical obturator for a ball valve and a ball valve for the controlled opening and closing of a fluid duct.
2. Description of the Related Art
So far it has been difficult to functionally achieve ball valves on the one hand with a linearisation of the rate of flow depending on the angle of rotation of the obturator to permit a gradual and controllable adjustment of the flow in the duct and on the other with a minimisation of the initial stroke of the obturator from the closed position (0°) to the angular position in which the passage of fluid commences. This second requirement is particularly felt for a fine adjustment of the flow which requires an angular adjustment stroke as large as possible, and to increase the speed of response of the valve to the adjustment, opening and closing commands.
DE102007025516 discloses a ball valve for the controlled opening and closing of a duct with:                a housing having an inlet and an outlet suitable for being connected to corresponding portions of the duct,                    a ball obturator housed in the housing in a rotatory manner around an adjustment axis and having an inner cavity with an inlet aperture and an outlet aperture suitable for being aligned with the inlet and outlet of the valve housing when the ball valve is open, as well as a third circular aperture between the inlet aperture and outlet aperture,            a control device suitable for being operated to rotate the obturator around the rotation axis,wherein the inlet aperture has a circular shape aperture and a central axis perpendicular to the adjustment axis, and the outlet aperture has an aperture (or transversal aperture cross-section) of a symmetrical shape to a plane orthogonal to the adjustment axis and parallel to the central axis and comprising a C-shaped rim section, two opposite sections of parallel rims connected to the ends of the C-section, two opposite, wedge-shaped inclined sections connected to the parallel sections, an arched section connected to the two inclined sections and projecting outwards from a parallel projection of the inlet aperture on the outlet aperture.                        
With this geometry of the ball obturator of the prior art, rapid opening and closing is achieved as well as an improved linearity of modulation (FIG. 7) compared to traditional ball valves (FIG. 6).
However the initial adjustment stroke with no flow is still considerable (around 15° . . . 20°) and the response of the obturator is still not sufficiently linear to permit rapid, controllable and intuitive (especially in the case of manual operation) adjustment, opening and closing of the valve.